1. Field of the Invention
The present invention relates to a method, an apparatus, and a system for transmitting information in a local area network (LAN), such as an Institute of Electrical and Electronics Engineers (IEEE) 802 network environment.
2. Description of the Related Art
With the widespread use of personal computers and the advances of the Internet, users use personal computers at home or offices to access a variety of servers over the Internet. The users download a diversity of content data, exchanges electronic mails, or participates in a chat system to exchange opinions through text data on a real-time basis.
Japanese Unexamined Patent Application Publication No. 2001-184292 discloses a technique of a chat system of the Internet in which a limited number of persons participating in a chat is allowed to concurrently listen to audio data.
Via a wide area network (WAN), users quickly acquire information at home or in offices, and smoothly exchange and share information. Communication technology has thus substantially advanced, providing convenient environments.
Sharing of files and printers is performed not only in a WAN but also in a LAN which is constructed in a limited area, such as home or offices, with personal computers and peripheral devices interconnected.
Known LANs employing universal asynchronous receiver-transceiver (UART) are unable to provide a sufficiently high data rate. It takes long time for the LAN to transmit or receive audio data requiring a data rate of about 1.4 MBps (Mbytes/s).
With universal serial bus (USB) introduced, personal computers transfer audio data from a USB connector. The maximum length of a USB cable is limited to 5 m. Under this limitation, a typical application of a peripheral device is a loudspeaker device of the personal computer used in the same room.
Communications in accordance with the today's widely used transmission control protocol/internet protocol (TCP/IP) not only achieve data rate and reliability in a performance level high enough to transfer audio data but also work with a cable extended to a maximum of 100 m in a LAN system installed at a home. Under these conditions, music is thus listened to everywhere in a wide area. With an apparatus, such as a network hub, the number of networked apparatuses is increased.
A plurality of pieces of audio data can be transferred at a time in view of communication bandwidth. If one server having a typical throughput is available, the server can concurrently supply client apparatuses in a plurality of rooms with audio data.
Personal computers and a variety of audio visual (AV) apparatuses, installed at a home, are connected via a LAN. Content data stored in a personal computer, such as audio data, video data, and AV data (containing audio data and video data synchronized with each other), are enjoyed on respective apparatuses in a living room, a study room, a bed room, etc.
As in the WAN system, a client apparatus receiving information issues a request to a server providing information in the LAN system in a typical operation mode. In response, the server supplies the client apparatus with desired information. In a LAN system with a plurality of client apparatuses configured therewithin, the client apparatuses access the server to concurrently receive the desired contents thereof.
In the case of the LAN system installed at a home, typically referred to as a home network, users may wish the personal computer working as a server to play the same content on the AV apparatus in each of the rooms, or in predetermined rooms only.
More specifically, the same audio data is transmitted to all rooms so that the same music is enjoyed in all rooms. Alternatively, the same audio data is transmitted to two rooms, which could be child's rooms. Rather than in response to a request from the client apparatuses, the server actively controls the client apparatuses.
The technique disclosed in Japanese Unexamined Patent Application Publication No. 2001-184292 for sharing the audio data can be used in a WAN system. However, in accordance with the disclosed technique, not only text data but also audio data is shared among participants in the Internet chat system. Without completing registration, any user cannot enjoy audio data as a supply destination in the chat group. Even a registered user cannot receive audio data unless the client apparatus of the user issues a request to transmit.
The technique disclosed in Japanese Unexamined Patent Application Publication No. 2001-184292 has no concept that a predetermined controller, such as a server, actively controls a client apparatus as a destination of content data. The disclosed technique thus fails to fully satisfy the need that the predetermined controller, such as the server, flexibly controls the client apparatus in accordance with intended usage.
In the home network LAN system, the client apparatuses are typically consumer electronics (CEs) dedicated to processing audio data and video data, including AV apparatuses, such as hard disk recorders. With a TCP/IP application running on such a client apparatus, it is advisable not to impose a large workload on the client apparatus.